Research is directed at investigating the cellular and genetic events that control T cell development. Transgenic and gene- targeting approaches are used to analyze the function of known genes and various molecular/genetic techniques (e.g.,RT-PCR, gene cloning) are used to identify novel genes that participate in thymocyte development. Current studies are directed at three major areas: (I) Role of T cell antigen receptor (TCR) signal transduction in thymocyte maturation. In mature T cells, the TCR transduces signals important for T cell activation and cell mediated immunity. In immature T cells, TCR signals are required for thymocyte development and for thymocyte(positive/negative) selection. The TCR is composed of multiple signal transducing subunits (the CD3 chains:gamma, delta and epsilon, and the zeta chain). These subunits couple the TCR to intracellular signal transduction pathways via conserved functional sequences termed Immunoreceptor Tyrosine based Activation Motifs(ITAMs)located in their cytoplasmic domains. To determine if the TCR signal transducing subunits perform distinct or analogous functions in development, we: a)generated zeta deficient and CD3-epsilon deficient mice by gene targeting, b) genetically reconstituted these mice with transgenes encoding wild-type or signaling- deficient forms of zeta and CD3-epsilon, and c) characterized the developmental and functional consequences of these alterations in TCR signaling potential. These studies revealed that expression of zeta-family and CD3 chains is necessary for normal T cell development but that no individual TCR signaling motif (ITAM) is specifically required. Thus the TCR signaling subunits appear to be functionally redundant. However, a direct relationship was observed between the number of TCR ITAMs and the strength of the TCR signal,indicating that the multiple ITAMs within the TCR function to amplify the signaling response. These results demonstrate a previously unappreciated role for the multiple TCR ITAMs, particularly during thymocyte selection, and identify an important function for signal amplification in generation of the mature T cell repertoire. (II) The role of other signal transducing proteins in T cell development has been examined by generating transgenic/knockout mice. These include CD5, a surface receptor distinct from the TCR that also contains an ITAM-like sequence but acts as a negative regulator of TCR signaling, and CD69, an early marker of T cell activation. (III) Genes that have potential functions in thymocyte development and/or T cell activation have been identified. A new lymphoid- specific kinase, Txk cloned in the lab has been shown to function in the TCR signaling pathway leading to calcium mobilization. A similar approach has been employed to identify other novel genes that may specify commitment of multipotent progenitor cells to the T cell lineage. - Immunology, T cells, Development, Transgenes, Gene trageting, Signal transduction.